Vertical Magnetic Field Diurnal as a Precursor to Earthquakes with Field Study in Parts of Western India

Vertical magnetic field (VMF) component of geomagnetic diurnal variation governed by the ratio of internal and external fields exhibits a 'V' shaped curve with minimum amplitude of about -30 gamma around 1200 hrs in the low latitude regions of the Earth on a solar quiet-day. This normal shape is signified by its phase inversion during stress accumulation and, in contrast, by phase amplification on sudden release of energy, corresponding to the development and loss of rock seismomagnetic field, resulting in a magnetic event of increase and decrease of the internal field. The normal diurnal reversion occurs in a stabilized strain condition. This characteristic feature of VMF diurnal phase inversion may serve as a precursor to tectonism and help in forecasting earthquake occurrences by a few days in advance.

Field studies carried out in parts of Western India in the area between latitudes 20°30" and 28°00"N during the years 1991 to 1995 show that VMF diurnal phase inversion attaining positive amplitude is invariably followed by earthquake occurrences within a few days in the region. These earthquakes are located in vicinity of the contact zone of Indian- Eurasian tectonic plates, Aravalli range, Delhi-Haridwar ridge and Western Ghat fault zone. Persistent prevalence of the diurnal phase fluctuation related to inversion-amplification-normal suggests that Western India is under strain due to tectonic forces acting upon it and, on exceeding the threshold limit of rocks, the stress energy is being released from time to time through geologically weak zones in form of tremorslearthquakes.